| 1. |
- Demidov, V. I., et al.
(författare)
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The analysis of probe I-V characteristics in a magnetized low-temperature plasma
- 2001
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Ingår i: Contributions to Plasma Physics. - 0863-1042 .- 1521-3986. ; 41:5, s. 443-448
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Tidskriftsartikel (refereegranskat)abstract
- The validity of probe theories based on the classical electron transport to probes in low-temperature magnetized plasma of the toroidal device `Blaamann has been demonstrated. The analysis was carried out for the conditions when global transport of charged particles in the device is anomalous, namely for magnetic field up to 0.3 T and pressure range 0.1 - 1 Pa. It was shown also that for the magnetic field larger than 0.1 T probes longer than 15 mm provide electron saturation current practically independent of probe potential, hence more accurate measurements of the plasma parameters. The experiments have revealed that application of long probes oriented parallel to the magnetic field may cause an anomaly of the I-V characteristics in the sense that a local increase of the electron current appears near the plasma potential.
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| 2. |
- Ratynskaia, Svetlana V., et al.
(författare)
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Measurements of plasma potential and electron temperature fluctuation in a low-temperature magnetized plasma
- 2001
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Ingår i: Contributions to Plasma Physics. - 0863-1042 .- 1521-3986. ; 41:5, s. 449-454
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of fluctuations of plasma potential and electron temperature in a toroidal magnetized plasma is carried out by applying a cylindrical probe with insulating end plugs oriented parallel to the B-field in conjunction with another cylindrical probe oriented perpendicularly. Coherency and cross-phase between (V) over tilde (f) and (T) over tilde (e) are estimated, and typically have values close to 0.6 and pi respectively. Power-law spectra are found for frequencies well above the poloidal rotation frequency with spectral index typically around 4.0 for (V) over tilde (f) and around 2.5 for (T) over tilde (e). The density gradient is above the threshold for flute interchange instability, and the results are consistent with theory and global numerical simulations of this plasma.
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| 3. |
- Antoni, V., et al.
(författare)
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Turbulence and anomalous transport in magnetized plasmas : Hints from the reversed field pinch configuration
- 2004
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 44:06-maj, s. 458-464
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Tidskriftsartikel (refereegranskat)abstract
- The properties of plasma turbulence in the outer region of the Reversed Field Pinch experiments RFX and EXTRAP-T2R are reviewed. The statistical properties of fluctuations in the range of scales relevant for transport are presented. The observation of coherent structures emerging from the background turbulence and their interpretation in terms of vortices is reported. The interplay between these structures and the mean ExB flow of the plasma is demonstrated with emphasis to the action on the preferential rotation direction. The effect on the particle transport induced by the background turbulence and by the structures is discussed. Finally the methods tested to control turbulence and to mitigate the related transport are illustrated and discussed.
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| 4. |
- Barankova, Hana, et al.
(författare)
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Reactive process and hysteresis effect in magnetron with magnetized hollow cathode enhanced target
- 2020
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Ingår i: Contributions to Plasma Physics. - : WILEY-V C H VERLAG GMBH. - 0863-1042 .- 1521-3986. ; 60:9
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Tidskriftsartikel (refereegranskat)abstract
- The hysteresis effect in the reactive process was investigated in the magnetron with a magnetized hollow cathode enhanced target (HoCET) in which the target is coupled with the hollow cathode magnetized by the magnetic field of the magnetron. The process, where both the magnetron and hollow cathode plasmas are combined, is compared to the magnetron sputtering. The hysteresis curve in the magnetized HoCET magnetron, recording the titanium emission intensity versus varying content of nitrogen in the gas mixture exhibits a local maximum on the increasing part of the curve. The hysteresis curve is shifted to lower contents of nitrogen than the hysteresis curve for the magnetron. It is concluded that more efficient utilization of the reactive gas takes place in this device.
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| 5. |
- Borodkina, I., et al.
(författare)
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An Analytical Expression for the Electric Field and Particle Tracing in Modelling of Be Erosion Experiments at the JET ITER-like Wall
- 2016
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Ingår i: Contributions to Plasma Physics. - : WILEY-V C H VERLAG GMBH. - 0863-1042 .- 1521-3986. ; 56:6-8, s. 640-645
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Tidskriftsartikel (refereegranskat)abstract
- A new analytical approximation for the electric potential profile in the presence of an oblique magnetic field and the analytical solution for the particle motion just before the impact with a plasma-facing surface are presented. These approximations are in good agreement with fluid solutions and the corresponding PIC simulations. These expressions were applied to provide effective physical erosion yields for Be, which have in a second step been used in ERO code simulations of spectroscopy at Be limiters of the JET ITER-like wall. These new analytical expressions lead to an increase of the effective physical sputtering yields of Be by deuteron impact up to 30% in comparison with earlier pure numerical simulations. (
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| 6. |
- Brodin, Gert, et al.
(författare)
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Wave Generation in a Warm Magnetized Multi-Component Plasma
- 2014
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 54:7, s. 623-625
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Tidskriftsartikel (refereegranskat)abstract
- The resonant interaction between three waves propagating perpendicularly to an external magnetic field in a plasma is considered. We present the explicit expressions for the three wave coupling coefficients of a warm multi-component plasma. The results of previous work on the generation of THz radiation by laser plasma interaction are significantly improved. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 7. |
- Drake, James R., et al.
(författare)
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Experimental studies of MHD dynamics in a RFP magnetically confined plasma
- 2004
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 44:06-maj, s. 503-507
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Tidskriftsartikel (refereegranskat)abstract
- Studies of non-linear dynamics of MHD tearing modes in the EXTRAP reversed-field pinch experiments [1] have demonstrated such phenomena as mode rotation, phase-locking and wall locking.
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| 8. |
- Hoelzl, M., et al.
(författare)
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Insights into type-I edge localized modes and edge localized mode control from JOREK non-linear magneto-hydrodynamic simulations
- 2018
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Ingår i: Contributions to Plasma Physics. - : Wiley-VCH Verlagsgesellschaft. - 0863-1042 .- 1521-3986. ; 58:6-8, s. 518-528
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Tidskriftsartikel (refereegranskat)abstract
- Edge localized modes (ELMs) are repetitive instabilities driven by the large pressure gradients and current densities in the edge of H-mode plasmas. Type-I ELMs lead to a fast collapse of the H-mode pedestal within several hundred microseconds to a few milliseconds. Localized transient heat fluxes to divertor targets are expected to exceed tolerable limits for ITER, requiring advanced insights into ELM physics and applicable mitigation methods. This paper describes how non-linear magneto-hydrodynamic (MHD) simulations can contribute to this effort. The JOREK code is introduced, which allows the study of large-scale plasma instabilities in tokamak X-point plasmas covering the main plasma, the scrape-off layer, and the divertor region with its finite element grid. We review key physics relevant for type-I ELMs and show to what extent JOREK simulations agree with experiments and help reveal the underlying mechanisms. Simulations and experimental findings are compared in many respects for type-I ELMs in ASDEX Upgrade. The role of plasma flows and non-linear mode coupling for the spatial and temporal structure of ELMs is emphasized, and the loss mechanisms are discussed. An overview of recent ELM-related research using JOREK is given, including ELM crashes, ELM-free regimes, ELM pacing by pellets and magnetic kicks, and mitigation or suppression by resonant magnetic perturbation coils (RMPs). Simulations of ELMs and ELM control methods agree in many respects with experimental observations from various tokamak experiments. On this basis, predictive simulations become more and more feasible. A brief outlook is given, showing the main priorities for further research in the field of ELM physics and further developments necessary.
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| 9. |
- Ivanova-Stanik, I., et al.
(författare)
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COREDIV and SOLPS Numerical Simulations of the Nitrogen Seeded JET ILW L-mode Discharges
- 2016
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Ingår i: Contributions to Plasma Physics. - : WILEY-V C H VERLAG GMBH. - 0863-1042 .- 1521-3986. ; 56:6-8, s. 760-765
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present the comparison of simulations with the numerical codes COREDIV and SOLPS5.0 for JET L-mode discharges with ITER like wall (ILW). The simulations have been performed for L-mode shots with and without nitrogen seeding (#82291 - 9) which are characterised by relatively low auxiliary heating power (P-NBI = 1.1 MW) and low electron density (n(e) = 2.35 x 10(19) m(-3)). Comparisons are made to the experimental measurements (e.g. radiation levels, plasma profiles) and the differences between the results from the two codes (e.g. temperature and density profiles at the outer divertor plate) are shown and discussed.
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| 10. |
- Joost, J.-P., et al.
(författare)
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Löwdin's symmetry dilemma within Green functions theory for the one-dimensional Hubbard model
- 2021
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986.
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Tidskriftsartikel (refereegranskat)abstract
- The energy gap of correlated Hubbard clusters is well studied for one-dimensional systems using analytical methods and density-matrix-renormalization-group (DMRG) simulations. Beyond 1D, however, exact results are available only for small systems by quantum Monte Carlo. For this reason and, due to the problems of DMRG in simulating 2D and 3D systems, alternative methods such as Green functions combined with many-body approximations (GFMBA), that do not have this restriction, are highly important. However, it has remained open whether the approximate character of GFMBA simulations prevents the computation of the Hubbard gap. Here we present new GFMBA results that demonstrate that GFMBA simulations are capable of producing reliable data for the gap which agrees well with the DMRG benchmarks in 1D. An interesting observation is that the accuracy of the gap can be significantly increased when the simulations give up certain symmetry restriction of the exact system, such as spin symmetry and spatial homogeneity. This is seen as manifestation and generalization of the “symmetry dilemma” introduced by Löwdin for Hartree–Fock wave function calculations.
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| 11. |
- Kagan, G., et al.
(författare)
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Neoclassical Theory of Pedestal Flows and Comparison with Alcator C-Mod Measurements
- 2012
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 52:5-6, s. 365 - 371
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Tidskriftsartikel (refereegranskat)abstract
- Neoclassical implications of the strong radial electric field, inherently present in an H-mode tokamak pedestal, are considered. The main ion poloidal flow in the pedestal is predicted to be reduced in magnitude, or even reversed, compared with its core counterpart. The resulting change in the neoclassical formula for the impurity flow is shown to result in improved agreement with boron measurements in the Alcator C-Mod pedestal. In addition, due to the ion flow being modified, the bootstrap current is expected to be enhanced in the pedestal over conventional predictions.
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| 12. |
- Lucco Castello, Federico, et al.
(författare)
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On the advanced integral equation theory description of dense Yukawa one-component plasma liquids
- 2020
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Ingår i: Contributions to Plasma Physics. - : Wiley-VCH Verlag. - 0863-1042 .- 1521-3986.
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Tidskriftsartikel (refereegranskat)abstract
- Different advanced bridge function closures are utilized to investigate the structural and thermodynamic properties of dense Yukawa one-component plasma liquids within the framework of integral equation theory. The isomorph-based empirically modified hypernetted-chain, the variational modified hypernetted-chain, the Rogers-Young, and the Ballone-Pastore-Gall-Gazzillo approaches are compared at the level of thermodynamic properties, radial distribution functions, and bridge functions. The comparison, based on accuracy and computational speed, concludes that the two modified hypernetted-chain approaches are superior and singles out the isomorph-based variant as the most promising alternative to computer simulations of structural properties of dense Yukawa liquids. The possibility of further improvement through artificial crossover to exact asymptotic limits is studied.
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| 13. |
- Lönnroth, J. -S, et al.
(författare)
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Integrated ELM modelling
- 2006
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 46:7-9, s. 726-738
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a short overview of current trends and progress in integrated ELM modelling. First, the concept of integrated ELM modelling is introduced, various interpretations of it are given and the need for it is discussed. Then follows an overview of different techniques and methods used in integrated ELM modelling presented roughly according to physics approached in use and in order of increasing complexity. The paper concludes with a short discussion of open issues and future modelling requirements within the field of integrated ELM modelling.
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| 14. |
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| 15. |
- Pusztai, Istvan, 1983, et al.
(författare)
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Radio frequency induced and neoclassical asymmetries and their effects on turbulent impurity transport in a tokamak
- 2014
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 54:4-6, s. 534-542
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Tidskriftsartikel (refereegranskat)abstract
- Poloidal asymmetries in the impurity density can be generated by radio frequency heating in the core and by neoclassical effects in the edge of tokamak plasmas. In a pedestal case study, using global neoclassical simulations we find that finite orbit width effects can generate significant poloidal variation in the electrostatic potential, which varies on a small radial scale. Gyrokinetic modeling shows that these poloidal asymmetries can be strong enough to significantly modify turbulent impurity peaking. In the pedestal the ExB drift in the radial electric field can give a larger contribution to the poloidal motion of impurities than that of their parallel streaming. Under such circumstances we find that up-down asymmetries can also affect impurity peaking.
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| 16. |
- Rothkaehl, H., et al.
(författare)
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Diagnostics of Space Plasma on Board International Space Station - ISS
- 2011
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 51:2-3, s. 158-164
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Tidskriftsartikel (refereegranskat)abstract
- Electromagnetic emissions observed in the nearest Earth environment are a superposition of natural emissions and various types of man-made noises. Also, as a consequence of catastrophic events on the Earth surface such as: thunderstorm activity, earthquakes, volcanic eruptions, electromagnetic signals are registered on board low orbiting satellites. Therefore, a more accurate physical description of such a complex and dynamic system calls for a long term multi-point and multi-scales coordinated monitoring of space environment. The aim of OBSTANOVKA experiment on board ISS station is to monitor and diagnose the electromagnetic radiation and property of plasma around station, to enable the development theory of near Earth plasma interaction and for application purposes in space technology. To achieve these goals the Plasma-Wave Complex (PWC) was designed and constructed. Radio Frequency Analyser (RFA) has been developed jointly by SRC PAS in Warsaw and by IRF in Uppsala. New design radio receiver for frequency band 0.1-15 MHz, with three electric and magnetic field component of antenna system on board ISS was designed to monitoring and investigate the ionospheric plasma property and artificial noises generated around ISS. The instrument can be also used for monitoring the electromagnetic ecosystem for space weather purpose. New digital technology of this instrument creates a excellent possibility for monitoring the electromagnetic emissions in space and time domain.
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| 17. |
- Salmi, A., et al.
(författare)
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ASCOT modelling of ripple effects on toroidal torque
- 2008
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 48:1-3, s. 77-81
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Tidskriftsartikel (refereegranskat)abstract
- Toroidal field ripple, delta=(B-max-B-min)/(B-max+B-min) in ITER will be relatively large, about 0.5% at the outer midplane. Due to the importance of toroidal rotation on plasma stability and confinement it is important to understand the consequences of a non-negligible ripple field on rotation. Guiding centre following Monte Carlo code ASCOT is used to evaluate the torque on plasma from co-current NBI in presence of toroidal magnetic field ripple. Simulations are made for a JET discharge from 2007 Ripple Campaign aimed to clarify the effect of ripple on fusion plasmas in preparation for ITER. ASCOT results show large reduction of torque from co-NBI and negative torque from thermal ions, which together could create a counter rotating edge plasma.
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| 18. |
- Tolias, Panagiotis, 1984-
(författare)
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On the Klimontovich description of complex (dusty) plasmas
- 2023
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 63:9-10
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Tidskriftsartikel (refereegranskat)abstract
- The numerous idealizations that are involved in the exact microscopic statistical description of complex (dusty) plasmas are discussed in detail. The two prevailing approaches in the Klimontovich description of dusty plasmas are reviewed in a pedagogical manner. The continuous phase space approximation is introduced, within which the more rigorous treatment should collapse to the more heuristic treatment. The plasma Klimontovich equations are shown to be identical, but there are marked differences in the dust Klimontovich equations whose origin is analysed in depth.
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| 19. |
- Vorontsov-Velyaminov, P. N., et al.
(författare)
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Calculation of Canonical Properties and Excited States by Path Integral Numerical Methods
- 2011
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 51:4, s. 382-385
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Tidskriftsartikel (refereegranskat)abstract
- Path integral Monte Carlo method in the expanded ensemble is used for calculation of the ratio of partition functions for different classes of permutations treating the problem of several interacting identical particles (fermions) in an external field. Wang-Landau algorithm is used for adjustment of balancing factors. For systems consisting of greater than two number of particles we propose an advanced variant of our approach which implies calculation of the ratio of positive and negative contributions to the partition function. Densities and energies of the sequence of excited states starting from the ground state for a system of non interacting quantum particles are calculated in turn, one by one, by means of considering systems with artificially excluded lowest energy levels and further obtaining of the ground state of each next system constructed in this way. The idea of evaluation of densities of excited states for a quantum system with interparticle interaction by evaluating density difference between systems of different number of noninteracting Fermi-copies of the system of interest is realized in terms of cyclic expansion formalism for a simple 2D system of two spinless fermions interacting via Coulomb repulsion.
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| 20. |
- Wiesen, S., et al.
(författare)
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Effect of PFC Recycling Conditions on JET Pedestal Density
- 2016
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Ingår i: Contributions to Plasma Physics. - : WILEY-V C H VERLAG GMBH. - 0863-1042 .- 1521-3986. ; 56:6-8, s. 754-759
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Tidskriftsartikel (refereegranskat)abstract
- There is experimental evidence that the pedestal dynamics in type-I ELMy H-mode discharges is significantly affected by a change in the recycling conditions at the tungsten plasma-facing components (W-PFCs) after an ELM event. The integrated code JINTRAC has been employed to assess the impact of recycling conditions during type-I ELMs in JET ITER-like wall H-mode discharges. By employing a heuristic approach, a model to mimic the physical processes leading to formation and release (i.e. outgassing) of finite near-surface fuel reservoirs in W-PFCs has been implemented into the EDGE2D-EIRENE plasma-wall interaction code being part of JINTRAC. As main result it is shown, that a delay in the density pedestal build-up after an ELM event can be provoked by reduced recycling induced by depleted W-PFC particle near-surface reservoirs. However the pedestal temperature evolution is barely affected by the change in recycling parameters suggesting that the presented model is incomplete.
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| 21. |
- Yaroshenko, V. V., et al.
(författare)
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Measurements of the dust-ion momentum transfer frequency and ion drag force in complex plasmas
- 2005
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Ingår i: Contributions to Plasma Physics. - : Wiley. - 0863-1042 .- 1521-3986. ; 45:04-mar, s. 223-228
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Tidskriftsartikel (refereegranskat)abstract
- A simple self-consistent method to estimate the effect of the streaming ions on microparticles in a positive column of a dc discharge plasma is presented. The momentum transfer frequency in dust-ion collisions and the ion drag force are determined within a wide range of gas pressures, p = 20 - 120 Pa. The method does not require a priory knowledge of the particle charge, but involves only the particle charge gradient which is recovered from the same experimental data. The method depends only on two experimental quantities: dust particle drift velocity and electric field, thus minimizing the errors in the estimates. Reasonable agreement is found between our force measurements and theoretical predictions, corresponding to the regime of moderate ion-dust particle coupling.
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| 22. |
- Zagorski, R., et al.
(författare)
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Modelling of JET DT experiments in ILW configurations
- 2018
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Ingår i: Contributions to Plasma Physics. - : WILEY-V C H VERLAG GMBH. - 0863-1042 .- 1521-3986. ; 58:6-8, s. 739-745
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Tidskriftsartikel (refereegranskat)abstract
- Numerical scan at constant shows that core and scrape-off layer (SOL) radiations do not depend on the plasma current (I-p). Whereas the SOL radiation increases with seeding, the core radiation, however, does not continue to increase with seeding but rolls over at higher seeding rates in the simulations. The core plasma contamination by W ions is low, c(W) << 10(-4). When the seeding starts, an increase in radiation power leading to a reduction in P-loss = (P-aux - P-rad) is observed, influencing the plasma confinement. The power scan at constant I-p indicates that the core radiation, P-plate, P-SOL (and even SOL radiation), saturates with seeding. In addition, strong dilution with increasing seeding (Z(eff) >> 3) and large W concentrations with increasing power are found. Comparing neon with nitrogen seeding, it is seen that neon leads to slightly larger total radiation than nitrogen. However, that is achieved with much higher plasma contamination (Z(eff) approximate to 4-5) and dilution in the case of Ne, and simultaneously the power crossing the separatrix is lower for Ne than for N, indicating better H-mode performance in N-2-seeded discharges.
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| 23. |
- Zagorski, R., et al.
(författare)
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Modelling of the JET DT Experiments in Carbon and ITER-like Wall Configurations
- 2016
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Ingår i: Contributions to Plasma Physics. - : WILEY-V C H VERLAG GMBH. - 0863-1042 .- 1521-3986. ; 56:6-8, s. 766-771
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Tidskriftsartikel (refereegranskat)abstract
- In this paper numerical simulations with the self-consistent COREDIV code of the planned JET DT experiments have been performed. First, record shot from the 1997 experiments was simulated and good agreement with experimental data has been found. Direct extrapolation of the carbon wall results to the new ILW configuration (discharge parameters as for the shot #42746) shows very good core plasma performance with even higher fusion power but with too large power to the divertor. However, with the neon seeding the heat load and plate temperatures can be efficiently reduced keeping good the plasma performance. Investigations have been done also for the planned DT operation scenario based on a conventional ELMy H-mode at high plasma current and magnetic field. Simulations for the reference ELMy H-mode shot #87412 show good agreement with the experimental data but the direct extrapolation of the DD results to deuterium-tritium operation shows relatively poor performance in terms of the achieved fusion power. The situation improves, if the highest heating power is assumed (41 MW) and fusion powers in the excess of 12 MW can be achieved. All the high performance shots require the heat load control by neon seeding which shows rather beneficial effect on the plasma performance allowing for relatively wide operational window in terms of the amount of the allowed neon influx.
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